This invention relates to busbars utilized in electrically powered cells. In particular, this invention relates to edge and internal busbars utilized in electrochromic devices. This invention also relates to edge and internal busbars that can be utilized in other electrically powered cells such as electroluminescent and photochromic devices, thin-film batteries, and other cells that use geometries similar to the electrochromic devices described herein. Further, this invention relates to control circuits and methods to control the coloration of such electrochromic devices through an intermittent application of power.
Electrochromic (EC) devices are devices in which a change in an electrical signal applied to the EC device results in a change in an optical property of the EC device. Typically, the optical property is optical transmittance, although other properties can be affected such as, for example, optical spectral distribution or polarization. Electrochromic devices can be used for many applications, such as rear view automotive mirrors, windows, sunroofs, shades or visors for automotive and mass transportation applications, architectural windows, skylights, displays, light filters and screens for light pipes, displays, and other electro-optical devices.
A variety of technologies exist for producing chromogenic members. xe2x80x9cChromogenic devicesxe2x80x9d, as used herein, is employed as commonly known in the art. Examples of these chromogenic devices include electrochromic devices, photochromic devices, liquid crystal devices, user-controllable-photochromic devices, polymer-dispersed-liquid-crystal devices, and suspended particle devices.
For example, electrochromic devices are discussed by N. R. Lynam and A. Agrawal in xe2x80x9cAutomotive Applications of Chromogenic Materialsxe2x80x9d, Large Area Chromogenics: Materials and Devices for Transmittance Control, Optical Engineering Press, Bellingham, Wash. (1989), incorporated herein by reference. Other pertinent references include N. R. Lynam, xe2x80x9cElectrochromic Automotive Day/Night Mirrorsxe2x80x9d, SAE Technical Paper Series, 87036 (1987); N. R. Lynam, xe2x80x9cSmart Windows for Automobilesxe2x80x9d, SAE Technical Paper Series, 900419 (1990); C. M. Lampert, xe2x80x9cElectrochromic Devices and Devices for Energy Efficient Windowsxe2x80x9d, Solar Energy Materials, 11, 1-27 (1984); JP 58-20729; and U.S. Pat. Nos. 3,521,941, 3,807,832, 4,174,152, 4,338,000, 4,652,090, 4,671,619, 4,702,566, 4,712,879, 4,793,690, 4,799,768, Re. 30,835, 5,066,112, 5,073,012, 5,076,674, 5,122,647, 5,142,407, 5,148,014, 5,239,406, and 5,657,149 each incorporated herein by reference.
Electrochromic panels are also discussed by Sapers, S. P., et al. in xe2x80x9cMonolithic Solid-State Electrochromic Coatings for Window Applicationsxe2x80x9d, Proceedings of the Society of Vacuum Coaters Conference (1996), incorporated herein by reference, with regard to devices of the type shown in FIG. 1E. Devices comparable to that shown in FIG. 1E, and having photovoltaic layers for self-biasing operation are also described in U.S. Pat. No. 5,377,037.
Other related references of interest include U.S. Pat. No. 5,241,411, U.K. Patent No. 2,268,595, Japanese Laid-Open Patent No. Appln. No. 63-106730, Japanese Laid-Open Patent No. Appln. No. 63-106731, and U.S. Pat. No. 5,472,643, each incorporated herein by reference. Also pertinent is International Application No. PCT/US 97/05791, incorporated herein by reference, which pertains to electrochromic devices that can vary the transmission or reflection of electromagnetic radiation by applying an electrical stimulus to an EC device. International Application No. PCT/US 97/05791 uses a selective ion transport layer in combination with an electrolyte having at least one redox active material to provide a high-performance device.
Also suitable for use in this invention are liquid crystal devices such as those described by N. Basturk and J. Grupp in xe2x80x9cLiquid Crystal Guest-Host Devices and Their Use as Light Shuttersxe2x80x9d, Large Area Chromogenics: Materials and Devices for Transmittance Control, Optical Engineering Press, Bellingham, Washington (1989), incorporated herein by reference.
User-controllable-photochromic devices (UCPC) are discussed in U.S. Pat. No. 5,604,626, entitled xe2x80x9cNovel Photochromic Devicesxe2x80x9d, incorporated herein by reference.
Polymer-dispersed-liquid-crystal (PDLC) devices are described by N. R. Lynam and A. Agrawal, xe2x80x9cAutomotive Applications of Chromogenic Materialsxe2x80x9d, Large Area Chromogenics: Materials and Devices for Transmittance Control, Optical Engineering Press, Bellingham, Wash. (1989), incorporated herein by reference.
Suspended particle devices are discussed in U.S. Pat. No. 4,164,365, incorporated herein by reference.
Examples of chromogenic devices that emit light are described in Applied Physics Letters, Vol. 71, page 1293 (1997).
Examples of chromogenic devices that can store image patterns due to a change in an optical property of a material are described in U.S. Pat. No. 5,744,267, incorporated herein by reference.
The general control of chromogenic devices is discussed in U.S. Pat. Nos. 4,793,690, 4,799,768, 5,007,718, and 5,424,898, incorporated herein by reference.
The phenomenon of prolonged coloration of chromogenic devices is discussed in U.S. Pat. Nos. 5,076,673 and 5,220,317, each incorporated herein by reference.
FIGS. 1A through 1E depict typical examples of known electrochromic devices, while FIG. 1F shows another known type of chromogenic device.
For example, FIG. 1A depicts a layered EC device which includes a substrate 101, transparent conductor 103, electrochromic (redox) medium 105, transparent conductor 103xe2x80x2 and substrate 101xe2x80x2.
FIG. 1B illustrates a layered EC device which includes a substrate 101, transparent conductor 103, EC layer 107, electrolyte (redox medium) 109, transparent conductor 103xe2x80x2 and substrate 101xe2x80x2.
FIG. 1C shows another layered EC device having a substrate 101, transparent conductor 103, EC layer 107, ion-selective transport layer 111, electrolyte (redox medium) 109, transparent conductor 103xe2x80x2 and substrate 101xe2x80x2.
Still another such EC device is shown in FIG. 1D. This device includes a substrate 101, transparent conductor 103, EC layer 107, electrolyte 113, counterelectrode 115, transparent conductor 103xe2x80x2 and substrate 101xe2x80x2.
FIG. 1E shows an EC device having a substrate 101, transparent conductor 103, EC layer 107, electrolyte (ion-conductive layer) 117, counterelectrode 115 and transparent conductor 103xe2x80x2.
A typical liquid crystal or PDLC device is shown in FIG. 1F. This device includes a substrate 201, transparent conductor 203, liquid crystal or PDLC medium 205, transparent conductor 203xe2x80x2 and substrate 201xe2x80x2.
Since the above chromogenic devices are known to those skilled in the art, a detailed explanation of the manner of construction and operation of such devices is not necessary.
In general, it is important to distribute the voltage to an electrochromic (EC) device uniformly in order to (i) maintain the uniformity of the coloration and bleaching of the EC device during changes between such states of coloration and bleaching, (ii) to improve uniformity in such colored and bleached states, and finally (iii) to enhance the kinetics of coloration and bleaching. As the size of an EC device increases, it becomes increasingly more difficult to maintain the desirable voltage distribution uniformity because increased size typically leads to increased resistance of various components. Such increased resistance results in voltage drops and current losses that adversely affects the uniformity of voltage distribution.
In other electrical devices, a particular spatial voltage distribution profile often is desired. As the size of such devices increases, similar to the example of EC devices, it also becomes increasingly more difficult to maintain the desired spatial voltage distribution profile because of the increasing electrical resistance of various components.
An applied voltage is commonly distributed at the periphery of EC devices through the use of an edge busbar which distributes an applied voltage to a surface conductor electrode. The applied voltage causes a response in a particular responsive property of an EC device. Consequently, spatial or temporal differences in the applied voltage will cause spatial or temporal differences in the responsive property. Ohmic losses along an edge busbar can therefore critically affect the even distribution of voltage, leading to undesirable non-uniformities in the coloration and bleaching of an EC device.
Furthermore, EC devices often employ thin film transparent conductors such as indium tin oxide (ITO) and doped tin oxides (DTO) for the surface conductor electrode. Such thin film transparent conductors are also used in a wide range of applications in other areas such as displays, solar cells, and liquid crystal devices. If the magnitude of the electrical currents in such devices is large, there can be a considerable electrical potential drop across the transparent conductor. Similar to the effect of voltage variations along an edge busbar, variations of voltage in thin film transparent conductors can also lead to spatial inhomogeneities in the device behavior as well as to slower overall device kinetics. Such effects become increasingly noticeable and problematic with increasing device area.
Another related aspect of electrochromic devices is that they are current consuming devices. Accordingly, it is advantageous for the transparent conductors, i.e., the surface electrodes, to be very conductive. For applications such as large area EC panels, where current consumption is large, it is particularly important that the transparent conductors possess high effective conductivities. Present conventional large-area EC devices fabricated from commercially available transparent conductors such as, for example, ITO and DTO, generally possess slow kinetics and often display nonuniform coloring. For example, large-area EC devices presently are often darker at the edges than in the center.
EC devices can be fabricated on one substrate as described in U.S. Pat. No. 4,712,879; J. Gordon H. Matthew et. al., Proc. of 3d Symposium on Electrochromic Materials, The Electrochemical Society, Proc. Volume 96-24, Pennington, N.J., 1997, p. 311; and Badding, M. E., et al., Proc. of a 3d Symposium on Electrochromic Materials, The Electrochemical Society, Proc. Volume 96-24, Pennington, N.J., 1997, p. 369, each incorporated herein by reference.
Electrochromic devices can also be made using two substrates as described in U.S. Pat. Nos. 4,761,061, 4,768,865, 4,902,108, 5,142,407, 5,231,531, 5,472,643, and U.S. patent application Ser. No. 09/155,601, filed Aug. 9, 1997, each incorporated herein by reference.
Prior art EC devices are also described in Lynam N. R., Agrawal, A., Automotive Applications of Chromogenic materials, in Large-Area Chromogenics: Materials and Devices for Transmittance Control, SPIE Optical Engineering Press, Bellingham, Wash., 1990, p. 46 and Lampert C. L., Selkowitz, S. E., Large-Area Chromogenics: Materials and Devices for Transmittance Control, SPIE Optical Engineering Press, Bellingham, Wash., 1990, p. 22, each incorporated herein by reference.
U.S. Pat. Nos. 5,202,787 and 5,151,824, each incorporated herein by reference, show the way busbars in an EC device are typically put on the substrate edges in the prior art. As shown in FIGS. 2, 3A, and 3B, taken from the referenced patents, in a commercial EC automotive mirror which features two substrates 2223 and 2224, or 3333 and 3334, the substrates are staggered slightly with respect to each other. Spring clips 2221 and 2222, or 3331 and 3332, of a conductive material such as a copper sheet or a beryllium copper coated with tin are clipped to the two staggered edges of substrates 2223 and 2224, or 3333 and 3334, in order to provide an electrical connection to substrates 2223 and 2224, or 3333 and 3334. The two substrates must be offset, or staggered, from each other in order to expose surfaces 2225 and 3335 for the attachment of clips 2221 and 2222, or 3331 and 3332. The surfaces 2225 and 3335 are minimized in order to maximize the optical throughput area of the devicexe2x80x94that is, to maximize the overlapping area of the two substrates. Accordingly, the prior art provides electrical connections at less than one half of the perimeter of each substrate.
When a potential is applied to the wire clips 2221 and 2222, or 3331 and 3332, only a small potential drop occurs in these clips because of their high conductivity. The small potential drop can be neglected for small dimensions. However, as the dimensions of the application increases, the potential drop can become significant. Such potential drops can be a problem because the potential drop comes at a cost to the potential available to the chromogenic elements themselves. Further, significant current flow can occur at the clips and clip junctions, thereby adversely adding to the overall current load.
The resistance of a typical wire clip used in commercial automotive mirrors that are about 12 inches (30 cm) in length is about 0.2 xcexa9. The conductivity associated with the clip depends on the intrinsic conductivity of the material, the geometric parameters of the clip (such as thickness, width and the length of the strip), and on the relevant contact resistance.
To demonstrate the current consumption in the EC devices, a commercial EC automotive mirror was colored by applying a DC step voltage of 1.4V. The mirror initially consumed a current of 3 mA/cm2, decreasing to 0.9 mA/cm2 in the fully colored state.
According to Hichwa, B.Pl, xe2x80x9cLarge Area Electrochromics for Architectural Applicationsxe2x80x9d, International Conference on Coatings on Glass, Saarbrucken, Germany, October 1996, an EC window device made from all thin films on a single substrate when powered at 1.8V showed an initial current consumption of about 2 mA/cm2 which decreased to about 1 xcexcA/cm2 in the colored steady-state. By assuming that such devices can be fabricated with the above current values scaling with size while keeping similar performance characteristics, the current consumption can be calculated for an EC automotive mirror and a single substrate EC window at different dimensions.
Table 1 shows the current consumption of the devices with two different active areas: (1) 6 inches by 6 inches (15 cmxc3x9715 cm) and (2) 12 inches by 12 inches (30 cmxc3x9730 cm).
Therefore, as the size of the EC device increases, the current loads that the electrodes must carry are substantially increased.
Table 2 shows the resistance characteristics of several materials and the resistance associated with a tape with a dimension of 1 meter in length, 2 mm in width and 0.1 mm in thickness. Table 2 also shows the resistance drop in these tapes when they carry 0.1, 1 and 10 A of current.
As seen in Table 2, several materials incur serious voltage drops across their resistance runs (for a specific geometry) for the amount of current that must be provided to the EC cell. Since EC devices are typically powered at 1 to 3 volts, the voltage drop can significantly affect the actual voltage applied to the EC material, causing increases in coloration and bleach times, and in certain devices, leading to nonuniform coloration in the steady state condition. The problem of the voltage drop, resulting from the electrode resistance, is compounded by the increase in current when the size of the device gets larger as seen previously in Table 1. This invention is particularly useful for those EC devices where the current consumption exceeds 0.1 A during either coloring or bleaching processes.
When chromogenic devices are fabricated using two coated substrates, the typical gap between the substrates is in the range of from 10 to 1000 micrometers. As the size of the devices increases, such as for a six inch by six inch (15 cmxc3x9715 cm) device, in order to increase the charge throughput and to distribute the charge uniformly, it is important that busbars be applied to as much of the device perimeter as possible.
One prior art approach for a rectangular device as shown in FIG. 4, is to offset substrates 3301 and 3302 simultaneously around two edges of a corner to provide two exposed L-shaped surfaces 3304. Then, busbars 3303 are attached in a conventional way.
In another prior art approach, busbars 5503 are applied on opposite edges of exposed surface pairs 5504 by employing the geometry as shown in FIG. 5 where the rectangular substrates 5501 and 5502 are pivoted from each other so that the long dimension of each rectangular substrate is parallel to the short dimension of the other rectangular substrate.
Neither approach provides busbar coverage of a substantial perimeter of a substrate. As used herein, xe2x80x9csubstantial perimeterxe2x80x9d means more than half of the perimeter of a substrate which is covered by a continuous busbar. For larger devices such as those bigger than about 6 inches (15 cm) in width and length, it is especially desirable to put the busbars all around the device, in a manner which covers a substantial perimeter of each substrate in order to provide the applied signal to the entire chromogenic panel evenly.
Nevertheless, as described above, as the length of the busbar run increases, the resistance undesirably increases. As a result, the prior art increases the thickness of the busbar material for large devices in order to increase the conductivity/unit length of the busbar in an attempt to maintain the desirably low resistance of the busbar. However, a major problem with the use of conventional busbars such as spring clips and wires for such large chromogenic applications arises when the thickness of the busbar exceeds the typical cell gaps. Even when the thickness of the busbar does not exceed the cell gap, the geometries of the prior art busbars and their placement limit the allowable increases to conductivities. Further, there may also be a problem around substrate corners when one continuous strip of the prior art busbar clip is used.
Another method with substantial coverage is provided all around the periphery, by using thin conductors, as shown in U.S. Pat. No. 5,066,112. However, in this case, the conductor thickness is limited by the gap between the substrates and its width.
Another approach is to make the two substrates dissimilar in size so that the edges of one substrate extend from all around the perimeter of the other substrate. In this configuration, conventional wire clip busbars can be used on the larger substrate. However, it is difficult to attach conventional wire clip busbars to the smaller substrate due to the limited gap available between the two substrates. The very close geometry could cause electrical shorting of the two substrates at the conventional wire clip busbar of the smaller substrate.
As noted above, in addition to the problem of voltage drops from the edge busbar clips, if the magnitude of the electrical currents in EC devices is large, there can be a considerable electrical potential drop across the thin film transparent conductor, leading to detrimentally slower overall device kinetics and spatial inhomogeneities in the EC device behavior. Therefore, for applications where current consumption is large, and especially where the area of the EC devices is large (e.g., chromogenic panels), it is particularly important that the transparent conductors possess large effective conductivities. Large-area EC devices fabricated from commercially available transparent conductors such as, for example, indium tin oxide (ITO) and doped tin oxide (DTO) generally possess slow kinetics and often display nonuniform coloring (e.g., darker at the edges to which the busbars are connected than in the center).
Values for the sheet resistance of commercially available transparent conductors such as ITO and DTO are typically greater than about 5 xcexa9/sq (the units are also commonly written as xcexa9/▪) to about 15 xcexa9/sq. Lower sheet resistances may be obtained by increasing the thickness of the transparent conductor, but this adversely affects the optical properties (e.g., increased haziness and/or diminished transmissivity) and also adds appreciably to the cost. It is desirable to form substrates which possess appreciably lower effective sheet resistance (can be less than 1 xcexa9/sq) at a cost that is attractive for applications such as those described above.
U.S. Pat. No. 5,293,546, incorporated herein by reference, describes a method for making a display device in which one of the electrodes is preferably a metallic grid. Preferred line widths were 20 micrometers with line spacings of 500 micrometers and line heights of 0.2 to 3 micrometers. The grid is then coated by a metal oxide (e.g., 1000 xc3x85 of ITO). The invention relates to displays in which high resolution processing equipment must be used for depositing the grid pattern. Thus the cost is high, particularly if large substrates such as 6 inchxc3x976 inch (15 cmxc3x9715 cm) or bigger are required because maintaining high precision in such a fine grid pattern over increasing areas is costly. Further, since these substrates must be over-coated with ITO, they are unable to use more cost effective, mass produced transparent conductors, such as mass produced ITO or inexpensive DTO deposited onto glass sheets in a float line.
U.S. Pat. No. 4,768,865, incorporated herein by reference, describes the use of a free-standing metallic grid as one of the transparent conductors. In this invention, the metal grid participates directly in the electrochemical reaction in the EC cell. However, for most EC devices, it is not desirable for the electron conductor also to participate in the reaction.
U.S. Pat. No. 5,724,176, incorporated herein by reference, describes the use of a counterelectrode for a smart window that contains a transparent substrate and a linear electrically conductive material formed on a surface of the transparent substrate. A layer of an electrochromic material is formed on the window""s surface, and a layer of an electrolyte is arranged between the counterelectrode and the electrochromic electrode and in contact with the layer of the electrochromic material. Various patterns are described for the placement of the linear electrically conductive material.
U.S. Pat. No. 5,066,111, incorporated herein by reference, describes laminated EC devices. A metal grid on a glass substrate is employed as one electrode and a longitudinal set of busbars, preferably composed of a metal foil such as copper, or an electroconductive ceramic frit deposited on glass or on the surface of an electro-conductive film, is employed as the other electrode. The electrochromic film is deposited over the second electrode. Thus, the metal foil or frit conductors of the U.S. Pat. No. 5,066,111 invention are always in direct contact with either the electrochromic coating or the electrolyte. However, such direct contact can decrease the device lifetime because of reaction between the coating and the electrolyte or electrochromic coating. Moreover, if put on glass and then coated with the transparent conductive coating (TCC), other problems can arise. Most importantly, the TCC is usually deposited in a thickness of less than 0.3 micrometers. In comparison, tapes or underlying frits, etc., are typically in thicknesses of 10 to 1000 times the thickness of TCC. Thus, vacuum methods that are typically used to coat TCC have difficulty getting a conforming coating that adequately covers the edges. The reference does not address the relationship of the busbar thickness and width to the device size.
POLYCHROMIC(trademark) solid films are described in European Patent Publication No. EP 0 612 826 A1, incorporated herein by reference. The reference describes how polychromic solid films may be used in electrochromic devices, particularly glazings and mirrors, whose functional surface is substantially planar or flat or that are curved with a convex curvature, a compound curvature, a multi-radius curvature, a spherical curvature, an aspheric curvature, or combinations of such curvature.
Often, a demarcation means, such as a silk-screened or otherwise applied line of black epoxy, may be used to separate the more curved, outboard blind-spot region from the less curved, inboard region of such electrochromic mirrors. The demarcation means may also include an etching of a deletion line or an otherwise established break in the electrical continuity of the transparent conductors used in such mirrors so that either one or both regions may be individually or mutually addressed. Optionally, this deletion line may itself be colored black. Thus, the outboard, more curved region may operate independently from the inboard, less curved region to provide an electrochromic mirror that operates in a segmented arrangement. As described in European Patent Publication No. EP 0 612 826 A1, upon the introduction of an applied potential, either of such regions may color to a dimmed intermediate reflectance level, independent of the other region, or, if desired, both regions may operate together in tandem.
An insulating demarcation means, such as demarcation lines, dots and/or spots, may be placed within electrochromic devices, such as mirrors, glazings, optically attenuating contrast filters and the like, to assist in setting out the interpane distance of the device and to enhance overall performance, in particular the uniformity of coloration across large area devices. Such insulating demarcation means, constructed from, for example, epoxy coupled with glass space beads, plastic tape or die cut from plastic tape, may be placed onto the conductive surface of one or more substrates by silk-screening or other suitable technique prior to assembling the device. The insulating demarcation means may be geometrically positioned across the panel, such as in a series of parallel, uniformly spaced-apart lines, and may be clear, opaque, tinted, or colorless, and appropriate combinations thereof, so as to appeal to the automotive stylist.
As described in European Patent Publication No. EP 0 612 826 A1, a demarcation means may be used that is conductive as well, provided that it is of a smaller thickness than the interpane distance and/or a layer of an insulating material, such as a non-conductive epoxy, urethane or acrylic, is applied thereover so as to prevent conductive surfaces from contacting one another and thus short-circuiting the electrochromic assembly. Such conductive demarcation means include conductive frits, such as silver frits like the #7713 silver conductive frit available commercially from E.I. du Pont de Nemours and Co., Wilmington, Delaware, conductive paint or ink and/or metal films. Use of conductive demarcation means, such as a line of the #7713 silver conductive frit, having a width of about 0.09375xe2x80x3 (0.238 cm) and a thickness of about 50 xcexcm, placed on the conductive surface of one of the substrates of the electrochromic device may provide the added benefit of enhancing electrochromic performance by reducing busbar-to-busbar overall resistance and thus enhancing uniformity of coloration, as well as rapidity of response, particularly over large area devices. However, the non-conductive layers are applied in a way which does not prevent the underlying frit lines from making contact with the electrolyte or electrochromic layers. Thus, this frit may potentially react, especially when coloring and bleaching potentials are applied.
As described above, electrochromic (EC) devices are used to reversibly vary the light transmission or reflection by application of an electrical voltage. Applications of electrochromic devices include windows for architectural use (windows, interior partitions, skylights, light pipes), windows in transportation (automobiles, trucks, planes, trains, boats, etc.), eye-wear, and displays (including large area signage).
Electrochromic windows in buildings can provide higher energy efficiency as compared to static transmission windows, while increasing the user comfort by controlling illumination and reducing glare. The same benefits can accrue for transportation uses where the user comfort is enhanced by reducing solar heat and glare during the day, while reducing the cooling load on the air-conditioner. In many of these applications the EC device can be required to be kept in a certain desired state of transmission for long periods of time. For example, a window may be kept in a darkened or bleached state for many hours of the day and may even be kept in this state for many days.
Thus, it is desirable to enhance the durability of EC devices that are used in this long single state mode, while reducing energy consumption of the EC devices. Reducing energy consumption is particularly useful in circumstances where solely a battery is used to power such a device and thus, it is important to ensure that the battery drain is minimized. Such circumstances include use in a car, aircraft, watercraft, or eyeware. One aspect of the present patent describes circuitry which addresses one or more of these issues.
U.S. Pat. No. 5,148,014, incorporated herein by reference, describes the use of a linear regulated power supply to power an EC mirror.
U.S. Pat. No. 5,193,029, incorporated herein by reference, describes the use of a Zener diode and transistor, which is essentially a linear regulation, to provide voltage to an EC mirror.
U.S. Pat. No. 5,220,317, incorporated herein by reference, describes the use of a voltage divider consisting of series resistors to scale down the voltage provided to EC elements.
Electrochromic devices which will benefit from this invention are well known in the art. For example, these are described in U.S. patent application Ser. Nos. 09/155,601 and 08/699,940, filed Apr. 9, 1997 and Aug. 20, 1996, respectively.
For those EC devices which are colored by applying a voltage, it would be desirable not to require applying continuously the coloring potential after the required coloration depth has been reached. Such continued application of the coloring potential, while promoting EC reactions, can also promote side reactions which could have detrimental effect on the device longevity. This applies for all EC devices which need to be maintained in a state of coloration that is different from their natural transmission state. The natural transmission state of an EC device is measured at equilibrium with no applied potential and when the potential difference between the opposing electrodes is zero.
Typically, the EC devices can be kept colored for a finite period of time when the coloring potential is removed, i.e., the color of the device will change towards its natural state over a period of time. This change could occur over a wide range of time intervals, from fast over several seconds or minutes, to as slow as extending up to many days, depending on the device. A device where this change is fast is said to have short xe2x80x9cmemoryxe2x80x9d and one where the change is slow is said to possess long xe2x80x9cmemoryxe2x80x9d. For example, U.S. patent application Ser. No. 09/155,601 discloses devices with long memories and compares them with devices that have short memories.
It is clear that is would be advantageous to be able to maintain a coloration setting without having to maintain an applied voltage to electrochromic devices because circuitry that allows intermittent adjustment of the voltage as needed to maintain a coloration setting would lead to lower power consumption in the device.
U.S. Pat. No. 5,384,578 (to Lynam et.al.), incorporated herein by reference, describes the use of intermittent voltages for continuously variable mirror and windows, but does not relate to changing the voltage-on or voltage-off periods and voltage-time shapes under different conditions as discussed in the present invention.
U.S. Pat. No. 4,298,970 (to Saegusa), incorporated herein by reference, describes a technique for utilizing an intermittent technique to drive EC displays with memory. The patent only describes bimodal displays which have only two states, i.e., colored and bleached states and does not discuss devices which need continuously variable light transmission across a continuum of transmissive states.
U.S. Pat. No. 5,007,718, incorporated herein by reference, describes a method of driving electrochromic elements by using a current stabilizing circuit and a voltage stabilizing circuit in tandem with a power supply to form a stabilized power source, and applying a gradually increased coloring voltage and a gradually decreased discoloring voltage to keep the current flow within predetermined amounts.
U.S. Pat. No. 5,365,365, incorporated herein by reference, describes an electrochromic system for controlling the color state by determining the charge needed to obtain a set color from the discharge potential of the system and the coloration set-point. An integrator measures the charge passing through the system and compares it to the charge to be transferred, which is measured by a differential amplifier which compares a discharge potential measured by a capacitor with a selected color set-point.
U.S. Pat. No. 5,231,531, incorporated herein by reference, describes an electrochromic system in which a voltage generator is connected to electrically conductive films by an electrical control circuit. The voltage generator receives a set-point from a control unit and generates a potential differences as a function of the temperature of the electrolyte.
This invention is related to edge and internal busbars that lower the overall effective resistance of electrical devices, particularly EC devices, thereby enabling large devices to maintain desirable electrical properties. The present invention describes the benefits of applying the busbars of the present invention to a substantial perimeter of an EC device, as well as the m aterials and processes to accomplish this.
As shown later, the contact points with the conductive coatings constituting the EC devices may be less than half of the perimeter, but the busbar of the present invention runs continuously for more than half of the device perimeter. The term xe2x80x9cbusbarxe2x80x9d refers to a conducting medium that provides a substantially uniform voltage to all those points on the device perimeter that are connected to the busbar. The busbar should be capable of carrying substantial current with a voltage drop of preferably less than {fraction (1/10)}th of the applied voltage, or a voltage drop less than that which causes a perceptible change in the kinetics of the device (rate of coloration and bleach) or in the depth of coloration.
The voltage drop should be less than that voltage drop which would cause a perceptible change in the kinetics or coloration properties of the device. Thus, for some particular devices, higher voltage drops can be accommodated so long as such perceptible changes do not occur. Generally, however, such voltage drops are less than {fraction (1/10)}th of the applied voltage.
The conductance of the edge busbar conductor is dependent on the cross-section, length and the intrinsic conductivity of the busbar material. Since the gap between the two substrates for a EC cell is limited, the thickness of the busbar conductors must be within the limitations imposed by the cell""s size. To maximize the EC device viewing area, the width of the conductor in the prior art is limited as shown in FIGS. 4 and 5, where the width is limited to the exposed areas 3304 and 5504. Typically, this width is less than 25 mm, preferably less than 10 mm, in order to maximize effective cell area. At times, this width can be on the order of less than 2 mm. Further, for a device made by substrates that are exactly stacked on one another and separated by a gap of 100 micrometers, the thickness of the conductor on each substrate located between the two substrates is typically limited to less than 50 micrometers.
The present invention teaches the use of materials and processes to deposit busbars on a substantial portion of the device perimeter while overcoming the geometric constraints described above. A copper conductor which is 35 micrometers thick and 3 mm wide exhibits a resistance drop of 0.16 xcexa9 per meter. Accordingly, for a device that is one meter square, a continuous conductor around the device periphery will exhibit a drop of 0.32 xcexa9 from one diagonal edge to the other. For a device that will carry a current as low as even one ampere, the drop of 0.32V at an applied potential of about 1.5V is significant. This can result in non-uniform coloration, slow kinetics, etc. In such devices, it is preferable to maintain the potential drop below {fraction (1/10)}th of the applied voltage or below any voltage that will cause a perceptible change in the color uniformity of the device or a decrease in the kinetics.
Since the current consumption of an EC device changes with time, particularly when step potentials are used, it is preferable that the potential drop in the busbar is kept within the limits described above during both the switching period and also when the steady state is reached. If other materials from Table 2 are used instead of copper, except for silver, the resistance drop will be even higher for the same busbar dimensions. Thus the geometry of the busbar (such as thickness and width) of the tape will have to be increased for best performance.
An object of the present invention is to overcome the prior art constraints on edge busbar effective resistance arising from the geometrical limitations of busbar length, width, and thickness. The present invention uses specific geometry, materials and processes to form the edge busbars.
This invention overcomes these geometrical limitations by forming a conductive path from the electrode on a front side of a substrate to the edges of the substrate and then extending this conductive path on to the back of the substrate. On the edge of the device, on the back, or on both the edge and the back, highly conductive paths such as reinforcing conductors may be employed to lower the busbar resistance. The conductive path from the front of the substrates to the back could be the continuation of the same material which is used for the transparent conductor, such as indium tin oxide, or can be fabricated from a different material, so long as dimension and conductivity requirements are met. That is, the conductivity must be effective to prevent a potential drop of 10% or a potential drop that would detrimentally affect the performance of the EC panel, while the dimensions must be effective to allow the substrates to maintain a close proximity to each other. Once the conductive path is formed on the back of the substrates, the geometrical limitations on the thickness and the width of the busbar conductor are relieved substantially.
Accordingly, the present invention provides an edge busbar for an electrical device, wherein the edge busbar comprises at least one electrically conductive connector portion effective to form an electrically conductive path from a surface of the electrical device, wrapping around a portion of an edge, to an opposite surface of the electrical device, and an electrically conductive perimeter portion in electrical contact with the connector portion, wherein the perimeter portion is peripherally on a substantial perimeter of the electrical device.
The connector portion of the edge busbar of the present invention can be continuous peripherally on a substantial perimeter of the electrical device, can be continuous peripherally on an entire perimeter of the electrical device, or can be composed of a plurality of connector portions. That is, the connector portion can wrap completely around an entire perimeter edge of the electrical device, can wrap completely around a substantial perimeter portion of the perimeter of the electrical device, or it can be a series of smaller portions that each wrap around smaller portions of the perimeter of the electrical device. Regardless, there is a perimeter portion of the edge busbar of the present invention which is peripherally on a substantial perimeter of the electrical device and connects to the various connector portion(s) of the present invention.
The front of a substrate is generally defined as the surface having the conductive electrode layer thereon.
In the case of a two substrate device, the front of a substrate is the surface facing the other substrate. In the case of a single substrate EC device, the front of a substrate is the surface facing the EC stack. In general, the layer of transparent conductive material is on the front of a substrate.
Although other parameters such as the conductivity of the transparent conductors (electron conductors), the ionic conductivity of the electrolyte layer, and the intercalation rate in the EC coating and other coatings if used, might also influence the kinetic parameters of EC devices, as shown above, the resistance of the edge busbar itself can have an important affect on the performance of the EC device. Accordingly, it is an object of the present invention to minimize the contribution of the edge busbars towards slowing the EC device kinetics. The edge busbars of the present invention may also assist in promoting a spatially uniform rate of color change during coloring and bleaching cycles.
In one embodiment of the present invention, an edge busbar includes a connector portion that has a separation or separating portion. However, the connector portion at each side of the separation is electrically connected by the conductive electrode coating layer of the electrical device. The separation is relatively small between the connector portions on each side of the separation, so that there is negligible resistance across the break. In other words, the separation is electrically bridged by the conductive electrode coating layer. This allows the connector portion to be effectively continuous peripherally about the entire perimeter of the electrical device even though separations exist in the connector portion. Advantages to this configuration include ease of manufacture and reduced complexity of design.
Busbars of the present invention can be advantageously used in pairs. Another embodiment of the present invention provides an edge busbar pair for an electrical device, each edge busbar comprising a connector portion and a perimeter portion, wherein each connector portion is effective to form an electrically conductive path from a front surface of a substrate, wrapping around a portion of an edge of the substrate, to an opposite back surface of the substrate. The perimeter portions being in electrical contact with its respective connector portion, and wherein each perimeter portion is peripherally on a substantial perimeter of each respective substrate, and wherein the front surfaces of each substrate face each other with each substantial perimeter proximate to and substantially opposite to the other substantial perimeter.
As discussed previously, each edge busbar of an edge busbar pair can be continuous peripherally on a substantial perimeter of its substrate, can be continuous peripherally on an entire perimeter of its substrate, or can be composed of a plurality of connector portions. It is advantageous for each edge busbar to be composed of a plurality of connector portions. It is particularly advantageous for each connector portion of each edge busbar to be in an alternating relation with connector portions of the other edge busbar. As shown later, when the connector portions are in such alternating relation, the thickness of the busbar material can be thicker than one half of the total gap distance between the substrates and yet still not cause an electrical short. Further, a sealant and/or an insulator can be added to assure against any shorting. Nonetheless, as explained earlier, thicker busbar material is desirable in order to maximize conductivity.
The present invention can be implemented for single substrate devices or dual substrate devices. The edge busbars of the present invention can be used singly as needed advantageously (as contrasted with the prior art). However, single substrate devices can nonetheless require a pair of edge busbars because such devices, as described earlier and as known in the art, often are made by forming an EC stack onto a substrate. In such cases, the EC stack requires a pair conductive electrodes as well as the substrate. Accordingly, both conductive electrodes have electrical signals applied to them which would benefit from the advantages of the edge busbars of the present invention.
In the present invention, an edge busbar is used having a portion that can be fabricated of any convenient material with an effective maximum thickness that can be inserted in the cell gap without shorting from touching with the other busbar or with the opposing conductive substrate. At the same time, the edge busbar of the present invention provides sufficient conductivity such that a negligible voltage drop (preferably less than one tenth of the applied voltage) occurs in the edge busbar. Further, the edge busbar of the present invention covers a substantial portion of the device perimeter and can include the internal busbars of the present invention.
The present invention also relates to the construction of substrates, especially transparent conducting substrates, which possess relatively large effective conductivities by the inclusion of internal busbars.
The present invention further relates to the use of the aforementioned substrates to construct affordable large area EC devices that can be used for architectural applications, (e.g. windows, partitions, skylights, diffuser panels, light pipes, etc.), automotive (windows, sunroofs, etc.) or other transportation (windows for planes, trains, buses, boats, etc.) applications, or signage applications (including large area displays such as those used at stock exchanges, airports and other such facilities).
The present invention also provides substrates which possess appreciably lower effective sheet resistances (can be less than 1 xcexa9/sq or xcexa9/▪) at a cost that is attractive for applications such as those described above.
The present invention teaches means for lowering the sheet resistance of thin film transparent electrically conducting assemblies for use in chromogenic devices, particularly electrochromic (EC) devices. The present invention permits the manufacture of EC devices which possess significantly improved kinetics with regard to coloration and/or bleaching, even for devices which possess relatively large active areas. The present invention also results in devices which possess considerably improved coloration and bleaching uniformity.
Most practical EC devices, as shown in FIG. 6, are comprised of an xe2x80x9cEC Assemblyxe2x80x9d 6601 which is effectively bound on either side by electronically conducting electrodes (ECE) 6602. Generally speaking, electrodes 6602 may be comprised of any of a variety of electronic conducting materials. Because EC devices are generally used to modulate light, however, at least one of the ECE 6602 should possess reasonable transparency at the wavelengths of interest (mirrors and many displays, e.g., typically possess only one transparent ECE; and window-type devices typically possess two transparent ECE""s). The present invention provides improved effective conductivity of transparent ECE""s in a manner readily integrated into the device structure.
The present invention forms internal busbars by providing strips of highly conductive material electrically connected to interior portions of a transparent ECE. The internal busbars add regions of increased conductivity into a transparent ECE, thereby lowering the overall effective resistance of the transparent ECE. Such lowered overall resistance leads to large device advantages.
The internal busbars of the present invention have increased conductivity compared to the transparent ECE when measured along the longitudinal direction of the conductive strips of the present invention. That is, in a top view of the transparent ECE with an internal busbar strip, when one compares a section of the conductive strip having a length L and a width W with a section of the transparent ECE also having the dimensions of Wxc3x97L, the conductivity of the Wxc3x97L section of the internal busbar will be higher than the conductance of the Wxc3x97L section of the transparent ECE, along either dimension L or W. Preferably the conductivity of the conductive strip will be greater than about 2 times the conductivity of the transparent ECE, more preferably greater than about 10 times.
The internal busbars of the present invention achieves such higher conductance by several ways. According to one embodiment of the present invention, materials having inherently higher conductivities are used for the busbars. According to another embodiment of the present invention, the busbar strips are made thicker than the surrounding transparent ECE. Such thicker strips can be embedded below the transparent ECE and/or into the underlying substrate. It is important that these twoxe2x80x94that is, the internal busbars and the transparent ECExe2x80x94are in electrical contact with each other (continuous or spatially intermittent). One may even use a material, to enhance or to tailor the electrical characteristics of this electrical contact, different from that material of the internal busbars or of the transparent ECE.
In another embodiment, the internal busbar strips are formed on a different surface from that surface which has the transparent ECE. Strip connecting portions connect interior portions of the transparent ECE or device with segments of the internal busbar strip. Such strip connecting portions can extend through the substrate. The internal busbars of this embodiment are nonetheless xe2x80x9cinternalxe2x80x9d because they connect to regions of the transparent ECE away from the periphery.
The present invention also is directed to circuitry which uses low power. Another object of the present invention are circuits which apply intermittent coloration power to EC devices in order to maintain or control the EC devicesxe2x80x2 coloration while compensating for the EC devicesxe2x80x2 inherent coloration decay without needing a constant application of coloration power.